1. Field of the Invention
The subject of the present invention is a device for detecting a conduit and for determining at least one characteristic of its content.
2. Description of the Related Art
In all apparatuses for treating blood by means of extracorporeal circulation, in which the patient's blood is circulated in a semipermeable-membrane exchanger (dialyser, filter for plasmapheresis or haemofiltration for example), it is important to be able to check during treatment, in a continuous manner, that the membrane of the exchanger has not suffered rupture, especially due to the effect of the transmembrane pressure created in the exchanger in order to cause plasmatic liquid to pass through the membrane from the blood compartment of the exchanger to the spent-liquid compartment.
A means commonly used for checking the integrity of the membrane of the exchangers used for the purposes which have just been mentioned consists in placing, on an outlet line from the spent-liquid compartment of the exchanger, a blood detection device in the liquid flowing in the line. Generally, these detection devices are also provided in order to detect the presence of the line, whatever its content (air or saline solution), as a sine qua non condition of operation.
German Patent 3 910 250 describes a detector of this type, comprising:
a seat for housing a first line portion, comprising a first and a second zone which are opposite each other with respect to the longitudinal axis of the line when it is housed in the seat; PA1 light emission means and reception means sensitive to the light emitted by the emission means, the emission means and the reception means being arranged in the first zone in order to have parallel emission and reception directions; and PA1 light deflection means arranged in the second zone in order to send back towards the reception means at least part of the light emitted by the emission means. PA1 a seat for housing at least one portion of the conduit, comprising a first and a second zone which are opposite each other with respect to a recess intended to receive the conduit; PA1 light emission means, arranged in the first zone, having a preferential emission direction oriented towards the recess and reception means, sensitive to the light emitted by the emission means, having a preferential reception direction oriented towards the recess; and PA1 first light deflection means for deflecting, in the direction of the first zone, at least part of the light emitted by the emission means, at least when a conduit containing a substantially transparent liquid is engaged in the seat; PA1 second light deflection means for deflecting, in the direction of the second zone, at least part of the light deflected by the first deflection means so that, when a conduit containing a substantially transparent liquid is engaged in the seat, at least part of the light emitted by the emission means reaches the reception means after having passed through the conduit at least twice obliquely with respect to a longitudinal axis of the recess. PA1 in the absence of a conduit in the seat, at least part of the light emitted by the emission means reaches the reception means after a single deflection: PA1 when a conduit containing a gas is engaged in the seat, the reception means receive practically no light coming from the emission means; and PA1 when a conduit containing a substantially transparent liquid is engaged in the seat, at least part of the light emitted by the emission means reaches the reception means after having passed through the conduit four times.
In the embodiments described, the deflection means are formed by two mirrors arranged so as to face each other and respectively making an angle of 45.degree. with respect to the emission direction and the reception direction. The light emitted by the emission means is reflected twice before reaching the reception means and the optical path between the emission and reception means is always the same, whether or not a line has been engaged in the seat, and whatever the nature of the fluid present in the line (gas or liquid). With this device, a difference in nature or in quality of the fluid present in the line (liquid or gas, liquid containing or not containing blood) is manifested, within the sensitivity limit of the reception means and of the signal processing circuit with which it is associated, by a different attenuation of the light emitted by the emission means in the region of the reception means.